Japanese Unexamined Patent Publication (Kokai) No. 8-173893 discloses a coating layer forming apparatus and a method to form a coated layer. An explanation will be given of the coating device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 8-173893 with reference to FIG. 1.
A coating device 100 shown in FIG. 1 is provided with a coating container 101 above a base material 104. The coating container 101 is filled with a coating solution 102. Below the coating container 101 at the two ends of the base material 104 is arranged a shaft bearing support plate 103 for rotatably supporting the base material 104. The shaft bearing support plate 103 was mounted on it a not shown drive motor. The drive motor makes the base material 104 rotate in the illustrated clockwise arrow direction R.
Since the coating solution 102 flows out from a nozzle of the coating container 101, the coating surface 105 of the base material 104 made to rotate by the not illustrated drive motor is coated on its entire surface as if being wrapped by it along with the rotation. To level the thickness of coating solution 102 coated on the surface to be coated 105, a blade 106 set to an inclined angle θ of 135° with respect to a tangential direction of rotation of the base material 104 is provided at the surface to be coated 105.
A front end 106a of the blade 106 is held at a clearance of 100 μm from the coating surface 105. Further, the front end 106a of the blade 106 is formed into a stepped portion so as to become thinner. The blade 106 is fixed to a block 107. The excess amount of the coating solution 102 coated on the base material 104 is collected by the blade 106 and made to flow downward via an inclined surface of the blade 106 while the not shown drive motor makes the base material 104 rotate five to six times at 200 rpm. A solution receiving mechanism 108 for accommodating excess amount of the coating solution flowing down from a rear end of the blade 106 is provided.
The coating device 100 is simply structured and operates by a single principle, but suffers from the following disadvantages.
Since the coating solution 102 accommodated in the coating container 101 is made to drop from the nozzle of the coating container 101 on to the coating surface 105 of the rotating base material 104 by the free-fall dropping method, the amount dropped changes in accordance with the amount and viscosity of the coating solution 102 accommodated. Therefore, to prevent insufficient coating, a large amount of the coating solution 102 is made to drip on to the coating surface 105 of the substrate 104 and the excess amount of the coating solution is removed by the blade 106 and stored in the solution receiving mechanism 108, but the amount of the coating solution 102 consumed becomes large—which is uneconomical.
If a large amount of coating solution 102 is deposited on the coating surface 105 of the substrate 104, it cannot be fully removed by the blade 106, a coating of a uniform thickness cannot be formed, and it becomes difficult to improve the quality of the coating by reducing the speed of the substrate 104. If the speed of the substrate 104 is increased, the time for forming the coating becomes longer and the productivity is lowered.
The blade 106 is attached inclined so as to guide the excess coating solution 102 to the solution receiving mechanism 108 along its surface, the blade 106 is inclined to a blunt angle θ=135° with the rotating coating surface 105 of the substrate 104. That is, the blade 106 only scrapes off the excess coating solution 10 of the surface of the coating surface 105 of the substrate 104. The coating solution 102, however, has viscosity, so the amount of coating solution removed by the blade 106 changes in accordance with its viscosity. The thickness of the remaining coating solution on the coating surface 105 also changes in accordance with the viscosity. In this way, the quality of the coating film has a large dependence on the viscosity.
As apparatuses other than the above coating layer forming apparatus, for example, Japanese Unexamined Patent Publication (Kokai) No. 10-26081 and Japanese Unexamined Patent Publication (Kokai) No. 5-147189 disclose a screen printing method to coat material on a piston or other members. In a screen printing apparatus, however, the thickness of coated layer of the coating material becomes thin. To form a coating layer obtaining a sufficient sliding function, repeated coating is necessary. Therefore, there are problems that multiple coating is required, the number of steps in the process is increased, an increase in the coating facilities becomes necessary, and that the process of production becomes expensive.